1. Field of the Invention
The present invention relates to a method of forming rotors for use in an electricity generator. More specifically, the present invention relates to a method for assembling rotors having permanent magnets mounted therein for use with an electricity generator having a fixed stator.
2. DESCRIPTION OF THE PRIOR ART
Transportable refrigeration units have long used rotors having permanent magnets as part of a generator within the refrigeration unit. The typical refrigeration unit of this nature must be adopted to be driven by a prime mover while the unit is being transported between several locations. The unit has a generator to provide electricity to power the various components within the unit. Typically the prime mover driving the rotor is also connected to the compressor of the vapor compression refrigeration system.
It has been found that a generator of the permanent magnet type operates to deliver a supply of current suitable for operating fan or blower motors without the use of brushes or other rotating electrical connections. Permanent magnet rotors have been assembled using a centrifugal casting method. This method includes stacking the magnets and the various laminations between two retaining discs and then riveting the top and bottom retaining discs loosely in place. The entire assembly is then rotated so that the magents and laminations are forced radially outward against each other. This rotation of the assembly is within a rotating mold and molten aluminum is cast within the mold during the rotation. This requires the pouring of molten aluminum from an open ladle into the mold and further requires that the internal components of the assembly be heated to approximately 1000.degree. F. during casting (See U.S. Pat. No. 2,485,474). It has been found that manufacturing quality is difficult to control using this method and that the number of rejects for failing to comply with the appropriate quality control standards is excessive.
U.S. Pat. No. 2,660,865 issued to Wilbur G. Durant and assigned to Transicold Corporation, now a division of the assignee corporation herein, shows the use of a permanent magnet rotor within an electrical generator of a transportable refrigeration unit.